Filtering separators with the features described above are especially well-suited for, among other things, the separating of particles that are not liable to agglomerate, whose diameter is less than 10 .mu.m, and whose settling speeds are correspondingly low. The reasons for this suitability lie in the following advantageous characteristic features of this filtering separator.
The chamber, which is movable in the clean gas area, prevents the resettling onto the filter elements of the particles that have a low settling speed and that have just been cleaned off following the reverse-flow cleaning, which lasts, for instance, about 0.5 seconds, a resettling that makes the continuous operation of a filtering separator significantly more difficult. The chamber keeps the connecting openings of the cleaned filter elements, and of the filter elements that are adjacent to these, separated from the low gas pressure that prevails in the clean gas area for a period of time that is long enough for the settling of the particles. The particles thus make their way to the area underneath the filter elements, and are carried out of the housing by means of apparatus that are part of the filtering separator.
The traveling chamber also prevents the filter material of the filtering elements, which has been puffed up in an outward direction by the pulsed reverse-flow cleaning, from afterwards striking back in a strongly accelerated manner against the spacing elements of the filter elements, so that particles remaining in the filter material are not flung into the clean gas area in the manner of a rug being beaten. Not until the traveling chamber passes the outlet openings of the cleaned filter elements with one of its two side edges, in a sliding manner as a result of the low travel speed of the chamber, are these filter elements again joined, with the clean gas area. The filter material, which had previously been puffed up, thus approaches the support elements relatively slowly, and comes to lie against them in a relatively gentle manner.
A prerequisite for utilization of both advantageous characterizing features is that the chamber wall facing the housing dividing wall lie sufficiently closely against the housing dividing wall during a stop by the chamber.
In German patent DE 31 11 502 C2, a filtering separator is described that, through careful execution of the design, can achieve the effects described above and that can be assessed in a positive manner. What is disadvantageous about this type of construction, however, are those characteristics described in the following.
Since the traveling chamber is enclosed with respect to the clean gas area, the injector or injectors must draw in the secondary flush gas, whose volume should be about four to five times greater than the volume of the compressed air that is released, by means of the injection of compressed air, through a relatively small number of filter elements. As a result, the injectors first and additionally must overcome the flow resistance of the filter elements in question during the drawing in of the secondary flush gas, and must thereafter increase the pressure of the secondary flush gas to such an extent that the reverse-flow cleaning of the filter elements to be cleaned takes place during continuous operation with sufficiently assured effectiveness. Further, the flow resistance of the filtering separator should not exceed the values established during its planning.
With regard to the aspect mentioned above, during utilization of filtering separators constructed in accordance with the above-cited German patent, problems arose particularly with the presence of a higher particle loading of the crude gas ahead of the filtering separator, for example in the order of magnitude of 10 g and above of particles with a low settling speed per m.sup.3.
As a consequence of this higher particle loading, the flow resistance of the filter elements increases relatively quickly after a reverse-flow flushing, and as a result, the amount of secondary flush gas drawn in by the injector during the reverse-flow cleaning decreases. In the case of a separator of this type that has been dimensioned in the usual way, the chamber must therefore travel periodically and stepwise at a faster rate, as a preventive measure, if, for example, the flow resistance of the filtering separator should or must remain limited to 150 mm of water (column).
The reduction of the time span for each of the chamber stops for the reverse-flow cleaning is, however, limited by the fact that if the chamber stops for too brief a period after a reverse-flow cleaning, each of which lasts for only a fraction of a second, the particles with a low settling speed cannot settle far enough downward towards the particle removal apparatus of the filtering separator.
The result of these constraints is that, by way of example, the filtering separator must be made with a larger filter surface area and/or the chambers must be made so wide that there are additional filter elements available for the filtering of the crude gas and/or for the drawing in of secondary flush gas. If it becomes necessary, additional injectors must be installed in the suction region of the chamber. The installation of a second traveling chamber in the filtering separator could also be considered. All of these measures have the disadvantage, however, that the set-up expenditure for the filtering separator becomes larger, as does the filter surface area that is not available for the filtration of crude gas, as well as the space requirements for the filtering separator. In addition, the use of compressed air increases as well.